1. Field of the Invention
The present invention relates to a particle diameter measuring apparatus and, particularly, to an apparatus for optically measuring a particle diameter.
2. Description of the Related Art
The following apparatuses are known as prior art apparatuses related to the present invention.
An apparatus comprising: a laser light source; a coherence reducing element which receives laser light emitted from the laser light source, reduces the coherence of the laser light and projects the laser light having reduced coherence; a light ring forming section which converts the light projected from the coherence reducing element into ring light; an internal reflection mirror which concentrates the ring light on a particle to be subjected to measurement and illuminates the particle; an objective lens which receives light scattered from the illuminated particle inside the ring light; a light receiving element which receives the scattered light through the objective lens; and a computing section which calculates the diameter of the particle on the basis of the intensity of the scattered light received by the light receiving element from a monotonously increasing function (see, for example, EP 1286152 A1).
An apparatus comprising: a sheath flow cell which transforms a particle suspension liquid flow into a narrow or flat flow surrounded by a sheath liquid; light emitting means which illuminates particles in the transformed suspension liquid flow; image pickup means which captures images of the illuminated particles; image analyzing means which analyzes the captured particle images; and display means; wherein the image analyzing means comprises calculating means which obtains data of the particles by measuring the area and perimeter of each of the captured particle images and calculates the diameter and circularity of each of the particles on the basis of the particle data, graph preparing means which prepares a histogram on the basis of particle size frequency data of the particle diameter, prepares a two-dimensional scattergram based on two parameters corresponding to the particle diameter and the circularity and causes the display means to display the histogram and the scattergram, storage means which stores the captured particle images, and particle image recalling means which causes the display means to collectively display the particle images stored in the storage means (see, for example, U.S. Pat. No. 5,721,433).
In recent years, there has been a demand for measurement of particles each having a diameter on a submicron order to the order of several tens of nanomicrons for precisely analyzing solid constituents of blood and urine, inorganic particles such as fine ceramic particles, pigment particles, cosmetic particles, toner particles and abrasive particles, and organic particles such as food additive particles. However, the prior art apparatuses are unsatisfactory in the accuracy of the measurement of such fine particles.